TMS320F280021: Byte Accesses with the C28x CPU

Mohamed Hashad

Part Number: TMS320F280021

I am using the TI C2000 to receive data via SCI from another MCU which is 8 bit addressable

The other MCU is sending to TI C2000 data in TWO bytes each is 8 bit and since TI C2000 is 16 bit addressable (the byte is 16 bit) I can only receive the data correctly if I duplicated the receive variable (so I receive in two variables each with size u_16) . The solution is working but I don't this is the best solution to do

Do you have a better solution please to receive the data correctly?

Thank you

over 2 years ago

0 Vince over 2 years ago

TI__Mastermind 19795 points

Hi Mohamed,

Thanks for your question!

As a starting note: If you'd like, you can actually just receive ONE byte at a time from the other MCU without any issue. It will still store in a single 16-bit variable by default, but I will address changing that to "two 8-bit variables" below.

If you are wanting to save space (because you don't want to use a 16-bit variable for an 8-bit value), you can simply store two 8-bit values in the upper and lower half of the 16-bit variables, using a bitwise OR and shift of the values. Similar to pseudo-code below:

uint16_t twoByteStorage;

// every other byte, store in upper half:

if (loopCount%2==0) { twoByteStorage = twoByteStorage | sciReadChar(*) << 8; } // store in upper half on even loop

else { twoByteStorage = twoByteStorage | sciReadChar(*); } // store in lower half on odd loop

Regards,

Vince

0 Arpan Mukhopadhyay over 2 years ago

Prodigy 237 points

Check out the compiler intrinsic int &__byte( int * array , unsigned int byte_index );
More info is in the document https://www.ti.com/lit/ug/spru514y/spru514y.pdf?ts=1663236721522&ref_url=https%253A%252F%252Fwww.google.com%252F

There was more info in https://software-dl.ti.com/ccs/esd/documents/c2000_byte-accesses-with-the-c28x-cpu.html but I can't open it now

0 Arpan Mukhopadhyay over 2 years ago in reply to Arpan Mukhopadhyay

Prodigy 237 points

As copied from e2e.ti.com/.../3820011

uint16_t data = 0xABCD;

uint16_t low_byte, high_byte;

low_byte = __byte(&data, 0);    //should load 0xCD to 'low_byte'
high_byte = __byte(&data, 1);   //should load 0xAB to 'high_byte

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TMS320F280021: Byte Accesses with the C28x CPU